BGP – Border Gateway Protocol

BGP protocol performs actions by maintaining IP networks table for the biggest network in the world – The Internet. The BGP protocol, as a code of behavior, supported core routing decisions over the Internet. Instead of using traditional IGP (Interior Gateway Protocol) metrics, BGP protocol relies upon available path, network guidelines and rule-sets for routing decision making purposes. And just for this feature, it is sometimes expressed as a reachability protocol. The main idea behind the BGP creation was to replace the EGP (Exterior Gateway Protocol) to permit a complete decentralized routing. NSFNET backbone is the best example of a decentralized system.

BGP protocol enables the Internet to act as a truly decentralized network system. All older BGP versions before version 4 have been obsolete. Main reason of BGP version 4 consistent utilization is its support for classless inter domain route finding. This protocol also uses route aggregation to reduce the routing table size.

What BGP does?

best possible routing path’s determination

Information cluster transportation, in packets form, over the internetwork. This method of packets transportation is relatively straightforward, when you will compare it to complex path determination method.

The Border Gateway Protocol basically runs best-path determination within networks. Therefore, the role of BGP in TCP/IP networks is to perform interdomain routing. This protocol works as an exterior gateway protocol, which is used to carry out routing between several self-directed domains and to swap the routing information amongst those systems. It connects almost all networks in the world into the biggest worlds network – Internet. Soon after BGP introduction, the Exterior Gateway Protocol (EGP) was outdated. BGP resolved those serious problems that were attached with EGP and provided the stability to Internet development.

BGP descriptions are available in several RFCs such as in RFC 1771, which describes the up to date version of BGP, named BGP 4. Moreover, RFC 1654 is expressed the 1st specification of BGP while RFCs 1105, 1163, and 1267 are specifying those BGP versions which where actual before BGP version 4. But from 2006, BGP version 4 specification is available in RFC 4271 form.

BGP Routing Processes

BGP can perform three different types of routing. These types are mentioned below as:

Inter-autonomous system type routing is possible either between two or more BGP routers which are on different ASs. Moreover, internetwork topology’s consistent view can be achieved by peering routers with BGP. BGP main function is to supply optimal routes within the Internet by doing path determination.

Intra-autonomous system type routing is required for a consistent system topology view. It is the function of BGP to decide, which routes should be advertised to outside ASs.

Pass-through autonomous system type routing can take place between two or more BGP routers so that networks traffic can be exchanged across autonomous systems.

BGP Packet Header Layout

BGP packet header is to be made of four parts: Marker (16 bytes in length), Length (2 bytes), Type (1 byte) and Data field of variable length.